KANO, Nigeria (AP) -- A coordinated series of bombings and gun attacks Friday claimed by a radical Islamist sect killed at least seven people in the largest city in Nigeria's Muslim north, witnesses said, threatening to engulf the whole region in violence.

Gunfire echoed through the city late into the night, as security forces turned away emergency officials from sites of the attacks. The scope of the assault suggested that the death toll would rise, as it also represent the first major attack by members of the sect known as Boko Haram on Kano, a city of more than 9 million people that holds the many dominant political and religious leaders for Muslims in Nigeria.

The attacks began at 5 p.m. Friday, following afternoon prayers as workers began to leave their offices in the sprawling, dusty city.

A massive blast at a regional police headquarters shook cars miles (kilometers) away, an Associated Press reporter said. The blast came from a suicide car bomber who drove into the regional headquarters compound and detonated his explosives, deputy superintendent of police Aminu Ringim said. The explosion tore away the headquarters' roof and blew out the building's windows.

Three blasts struck other police stations around the city, said Abubakar Jibril, an official with Nigeria's National Emergency Management Agency. Gunfire also echoed through the streets.

A separate blast also struck the local headquarters of the State Security Service, Nigeria's secret police, witnesses and state-run television said. Secret police spokeswoman Marilyn Ogar declined to comment.

Inmates at the regional police headquarters fled amid gunfire, witnesses said. Witness Garba Danazumi Lere said he saw the dead bodies of at least three police officers and a local journalist there.

At a nearby passport office, at least three immigration officers and an unknown number of civilians also were killed, local Nigeria Immigration Service spokesman Mohammed Kanoma said.

Yushau Shuaib, a spokesman for Nigeria's National Emergency Management Agency, simply described the attack as "scary."

"Rescue workers evacuating victims to hospitals," Shuaib wrote in a text message. "No official casualty figures for now."

A spokesman for the Nigerian Red Cross said his organization likely would not have information until Saturday morning.

State authorities declared a 24-hour curfew as residents hide inside their homes amid the fighting.

A Boko Haram spokesman using the nom de guerre Abul-Qaqa claimed responsibility for the attacks in a message to journalists. He said the attack came as the state government refused to release Boko Haram members held by the police.

The assault comes as Nigeria's weak central government faces a rising threat from the group. The sect has carried out increasingly sophisticated and bloody attacks in its campaign to implement strict Shariah law across Nigeria, a multiethnic nation of more than 160 million people.

Boko Haram, whose name means "Western education is sacrilege" in the local Hausa language, is responsible for at least 510 killings last year alone, according to an Associated Press count. So far this year, the group has been blamed for at least 76 killings, according to an AP count.

Boko Haram's targets have included both Muslims and Christians. However, the group has begun specifically targeting Christians after promising it will kill any Christians living in Nigeria's predominantly Muslim north. That has further inflamed religious and ethnic tensions in Nigeria, which has seen ethnic violence kill thousands in recent years.

Friday's attacks also could cause more unrest, as violence in Kano has set off attacks throughout the north in the past, including postelection violence in April that saw 800 people killed. Kano, an ancient city, remains important in the history of Islam in Nigeria and has important religious figures there even today.

Authorities previously believed they destroyed Boko Haram in 2009, after a riot and ensuing security crackdown in Nigeria's northeast killed 700 people, including its then-leader Mohammed Yusuf. The group began to re-emerge in 2010, as authorities blamed motorcycle-riding gunmen from the sect for targeted assassinations.

However, the sect's attacks have grown more complex and deadly over time. Boko Haram claimed responsibility for an August suicide car bombing that targeted the U.N. headquarters in the capital, killing 25 people and wounding more than 100. The sect killed at least 42 people during a series of attacks Christmas Day in Nigeria that included the bombing of a Catholic church outside the country's capital Abuja.

In a video released last week, Imam Abubakar Shekau, Boko Haram's current leader, said the government could not handle attacks by the group.

Although President Goodluck Jonathan, a Christian from southern Nigeria, has declared emergency rule in some regions, the sect is blamed for almost daily attacks. Jonathan also has said he believes the sect has infiltrated security agencies and government offices in the country, though he has offered no evidence to back up the claim.

The attacks also serve as another embarrassment for Nigeria's federal police force. Earlier this week, police officials acknowledged the mastermind of the Catholic church bombing at Christmas had escaped custody.